1. Technical Field
The present invention relates to a scan-type optical apparatus.
2. Related Art
Recently, there is an increasing demand for a projector which is small-sized and produces high-quality images. In addition, with the developments of high output semiconductor laser and blue and green lasers, projector and display containing laser beam source for emitting laser beams are being developed increasingly. These devices can greatly widen the color reproduction range since they have a narrow wavelength range of the light source. Moreover, the projector and display including the laser beam source can reduce the size of the entire apparatus and the number of the components, and therefore have great potentialities as display apparatus for the next generation. Furthermore, the laser beam source has higher light emitting efficiency than that of a discharge lamp such as a known extra-high pressure mercury lamp, and thus contributes to power-saving of the apparatuses.
A certain type of display apparatus using a laser beam source device modulates the intensity of respective laser beams by two-dimensional laser beam scan to produce a picture image. For example, this display apparatus synthesizes R, G and B lights emitted from different laser beam source devices for generating the corresponding color lights into one light, and conducts scan of the resultant light using an optical scan device to display a picture image on a screen or the like.
For displaying a visually and completely recognizable image by using the laser beam source, it is necessary to increase the intensity of the laser beams emitted from the laser beam source to a certain level or greater. Thus, when a scan optical system of the image display apparatus stops for some reason, the laser beams continue to illuminate one point and therefore possibly damages the illuminated surface. Thus, a projector which prevents emission of laser beams from a housing of the apparatus when a scan unit stops for some failure has been proposed (for example, see JP-A-2004-312347 (Patent Document 1)).
The projector disclosed in this JP-A-2004-312347 includes a laser beam source, a scan unit, and a hold unit for stopping the scan unit at a predetermined position and holding the unit at that position. The hold unit of the projector constantly applies load to the scan unit. The load is given to the scan unit such that the laser beams can be compulsorily directed toward the outside of the housing opening when the scan unit stops for some reason. By this method, the hold unit prevents emission of the laser beams out of the housing of the projector when the scan operation of the scan unit is under an abnormal condition.
The scan unit has an MEMS scanner capable of providing sufficient scan speed. The MEMS scanner is driven by a device utilizing electrostatic force or a piezoelectric device.
However, the following problems arise from the above related art. According to the display apparatus disclosed in JP-A-2004-312347, an external force is given to the scan unit to divert the optical axis and thus prevent emission of the laser beams out of the housing when the scan unit stops for some failure. However, this method requires complicated structure and thus is difficult to be put to practical use.
In addition, when the MEMS mirror which generally performs reciprocating rotation is used in the scan unit, the neutral, position of the MEMS mirror having no breakage of its torsion bar is positioned at the center of the scan range. When a light blocking plate is equipped at the neutral position, for example, the center of the scan range is unusable and the display performance thus lowers. Moreover, it is generally hard to achieve compatibility between a deflection angle and a scanning speed in the MEMS scanner, and thus is difficult to obtain a sufficient deflection angle for achieving a necessary scanning speed.